Distributed computer systems utilize the technique of distributing application execution. More specifically, an application server locally executes an application program and provides the application output data to clients/network users who then display the results on a display screen that is locally-coupled to their local computer. Distributed systems can make the best use available computing resources, i.e., the more capable server performs compute and memory intensive application processing functions while, the client that may be less capable computationally but potentially more capable with respect to video performance, displays the output. In one type of distributed computing system, a user of the client views application output data on a local display during the execution of the application program and interacts with the application program via keyboard, mouse inputs, or other device inputs. The user's inputs correspond to requests to the application server to perform certain actions that affect the operation of the application program. The application server passes these requests to the application for further processing. The application server also intercepts application output data generated by the application program, and typically targeted to the operating system of the application server, and transmits all or part of the data to the client for display. From the perspective of the user, the application program seems to be executing locally even though it is actually being executed on a remote server and displayed locally.
There are various protocols that provide the above-described functionality. One example of such a protocol is the Remote Desktop Protocol (“RDP”) distributed by Microsoft Corporation of Redmond, Wash. RDP is based on, and an extension of, the ITU T.120 family of protocols. RDP is a multiple-channel capable protocol that allows for separate virtual channels carrying device communication and presentation data from the application server, as well as encrypted client mouse and keyboard data. RDP uses its own video driver to render display output by constructing the rendering information into network packets using RDP protocol and sending them over the network to the client. On the client, RDP receives rendering data and interprets the packets into corresponding Microsoft Win32 graphics device interface (GDI) API calls. For the input path, client mouse and keyboard events are redirected from the client to the server.
Another protocol that provides similar functionality is the Independent Computing Architecture (“ICA”) sold by Citrix Systems of Ft. Lauderdale, Fla. ICA is a protocol that enables separate screen updates and user input processing from the rest of an application's logic. All application logic executes on a first computing system and only screen updates, mouse movements, and keystrokes are transmitted during a session between the displaying computing system and the first computing system.
Distributed application processing systems have performed well for typical, office applications. However, certain applications that are graphically intense can adversely affect the performance of a distributed application processing system. Examples of graphically intense applications can include, but are not limited to, computer-aided drafting (“CAD”) applications, video editing applications, and computer games. In these graphically-intense applications, display updates typically require a large amount of bandwidth because they are large, bitmap images. This problem is exacerbated when an executing application program sends multiple display updates in a short period of time, such as when a CAD/CAM program rotates a three-dimensional model of a device for the user to view. The delay in output due to the large size of the respective screen updates adversely affects user experience and interaction with the application program and makes use of the application program impractical in a distributed application processing environment.